Wireless communication systems, for example cellular telephony or private mobile radio communication systems, typically provide for radio telecommunication links to be arranged between a plurality of base transceiver stations (BTS) and a plurality of subscriber units. An established harmonised cellular radio communication system, providing predominantly speech and short-data communication, is the Global System for Mobile Communications (GSM). GSM is often referred to as 2nd generation cellular technology.
An enhancement to this cellular technology, termed the General Packet Radio System (GPRS), has been developed. GPRS provides packet switched technology on GSM's switched-circuit cellular platform. A yet further enhancement to GSM that has been developed to improve system capacity can be found in the recently standardised Enhanced Data Rate for Global Evolution (EDGE) that encompasses Enhanced GPRS (EGPRS). A still yet further harmonised wireless communication system currently being defined is the universal mobile telecommunication system (UMTS). UMTS is intended to provide a harmonised standard under which cellular radio communication networks and systems will provide enhanced levels of interfacing and compatibility with many other types of communication systems and networks, including fixed communication systems such as the Internet. Due to this increased complexity, as well as the features and services that it supports, UMTS is often referred to as a third generation (3G) cellular communication technology. In UMTS, subscriber units are often referred to as user equipment (UE).
Within GSM, two modes of operation (e.g. two modulation schemes) may be used, Gaussian Minimum Shift-keyed (GMSK) modulation and 8-phase shift keyed (8-PSK) modulation. GMSK is a constant amplitude phase modulation scheme whilst, for the second generation (2G) standard, 8-PSK incorporates both amplitude and phase modulation.
In such cellular wireless communication systems, each BTS has associated with it a particular geographical coverage area (or cell). The coverage area is defined by a particular range over which the BTS can maintain acceptable communications with subscriber units operating within its serving cell. Often these cells combine to produce an extensive coverage area.
Wireless communication systems are distinguished over fixed communication systems, such as the public switched telephone network (PSTN), principally in that mobile stations/subscriber equipment move between coverage areas served by different BTS (and/or different service providers). In doing so, the mobile stations/subscriber equipment encounter varying radio propagation environments. In particular, in a mobile communication context, a received signal level can vary rapidly due to multipath and fading effects.
One feature associated with most present day wireless communication systems allows the transceivers in either or both the base station and/or subscriber unit to adjust their transmission output power to take into account the geographical distance between them. The closer the subscriber unit is to the BTS's transceiver, the less power the subscriber unit and BTS's transceiver are required to transmit, for the transmitted signal to be adequately received and decoded by the other unit.
Thus, the transmit power is typically controlled, i.e. set to a level that enables the received signal to be adequately decoded, yet reduced to minimize potential radio frequency (RF) interference. This ‘power control’ feature saves battery power in the subscriber unit. Initial power settings for the subscriber unit, along with other control information, are set by the information provided on a beacon (control) physical channel for a particular cell.
Furthermore, in a number of wireless communication systems, the effect of fast fading in the communication channel is a known and generally undesirable phenomenon caused by the signal arriving at a receiver via a number of different paths. Therefore, fast power control loops are often adopted to rapidly determine and optimize the respective transmit power level.
It is known that, within the field of power control techniques, closed loop control systems are widely adopted but suffer from the following problems:                (i) With the power amplifier (PA) fully off, and with no radio frequency (RF) output the loop is in a highly nonlinear state and cannot be controlled by a linear closed loop control system. A simple economical activation scheme, where the output power is increased to a desired minimum that will allow effective linear closed loop control, is required.        (ii) Transitioning from the activation state into the closed loop state can result in undesirable transients.        (iii) The inventors of the present invention have recognised and appreciated that the initial value of the closed loop reference can impact the switching transients. A simple and automatic mechanism for setting this initial value is required.        (iv) A raised cosine type waveform is typically employed as the reference; as it can be shown to best satisfy both the transient and spectral specifications. However, application of a log detector as the power detection mechanism will distort the desired raised cosine profile at the PA output and compromise spectral emission performance. Hence, a scheme to avoid this log distortion is therefore required.        
In the area of activation/turn-on of the power amplifier (PA), it is also known that minimising transient interference is critical. It is known that some PA power control systems utilise a log detector instead of a peak detector. A log detector design provides an extended closed loop power control range as compared to a peak detector. In practice this extended range is used to simplify the activation or turn on of the PA, e.g. in general the loop can therefore be closed at a relatively lower power with a log detector compared to a peak detector.
Additionally, there is a linear relationship between output power and detected voltage (in the form of V/dBm), when using a log detector design. The linear relationship facilitates much easier calibration or phasing of the target power (PWR).
Where a peak detector is used, the activation process is non-linear and requires a more complex signal to be applied to the bias point, for example in the case of a Gaussian Minimum Shift Keyed (GMSK) bias control system. In addition, the more complex waveform used with a peak detector typically needs to be calibrated/phased in the factory with respect to output target power.
Thus, in the area of PA activation, there exists a need to turn on the PA at a sufficiently low power so that any transients that are generated do not exceed the PvT specification.
Thus, critical standards' test specifications may be failed if accurate control of ramp generation and PA activation/turn on is not achieved, such as:                (i) Power versus time (PvT), or        (ii) Out-of-band spectral emission performance.        
A need therefore exists, in general, for an improved power control arrangement and method of operation, wherein the abovementioned disadvantages may be alleviated.